This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-151389, filed May 21, 2001; and No. 2001-322065, filed Oct. 19, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a silver halide emulsion that is excellent in the ratio of sensitivity/granularity and is useful as, in particular, an emulsion for forming a blue-sensitive layer.
2. Description of the Related Art
In the field of silver halide photographic lightsensitive materials, silver halide tabular grains have become to be used widely because of their many advantages; their recent technical development is remarkable.
As a composition of silver halide grains, silver iodobromide (also including silver iodochlorobromide)-based compositions are mainly employed in color photographic lightsensitive materials except color paper. A silver iodobromide grain contains silver iodide in a silver bromide crystal lattice in an amount not more than a solid solubility limit in the silver bromide (that is, at a silver iodide content not more than 40 mol %). Silver iodobromide has advantages over silver bromide, such as improvement in latent image-forming efficiency, improvement in light absorption (absorption inherent to silver halide), improvement in adsorption of addition adsorbant, and improvement in graininess. On the other hand, drawbacks of silver iodobromide include inhibition of development and chemical sensitization inhibition. Many researches have been made to solve such drawbacks. In Duffin, Photgraphic Emulsion (Focal Press, 1966) p. 18, there is a statement xe2x80x9cIn the case of silver iodobromide emulsions, an important factor to be considered is the position of an iodide. An iodide may be present mainly in a central region of a crystal, throughout a grain or mainly in a perimeter surface. The practical position of an iodide depends on preparation conditions and have clear effects on physical and chemical characteristics of a crystal.xe2x80x9d A core-shell silver iodobromide emulsion is a technology for overcoming the drawbacks of the aforementioned silver iodobromide and for improving photographic properties and has been recognized in the art. U.S. Pat. No. 1,027,146 describes the concept of that emulsion. Bndou et al., xe2x80x9cPhotographic Silver Halide Emulsion Containing Double Structure Grainsxe2x80x9d J. Imag. Sci., Vol. 29, No. 5, 193-195 (1985) demonstrates the fact that a grain of a double structure shows an enhanced blue absorption and exhibits a good development activity due to an octahedral structure.
On the other hand, the fact that silver iodobromide grains have a microscopic distribution of silver iodide has been reported by M. King et al. in xe2x80x9cProgress in Basic Principles of Imaging Systems,xe2x80x9d reported in International Congress of Photographic Science held in Cologne (1986) and by Y. T. Tan et al., in SPSE, the 41st annual meeting. In Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-)1-183644, a silver halide grain having no microscopic distribution of silver iodide and having a completely uniform silver iodobromide layer has been disclosed.
Since the absorption of blue light is increased when the silver iodide content in a silver iodobromide grain is increased, silver halide grains having a high silver iodide content are suitable for an emulsion to be used particularly for a blue-sensitive layer.
In formation of tabular grains having a high silver iodide content, grain formation has become more difficult, for example, a distribution of silver iodide contents between grains has become greater or a distribution of grain sizes has become greater.
In JP-A-6-332092, a silver halide emulsion having a narrow distribution of silver iodide contents between grains is disclosed. JP-A-11-174606 describes a tabular silver halide grain emulsion having a silver iodide content of from 4 to 15 mol %, a thickness of 0.07 xcexcm or less, and a variation coefficient of projected area diameters (diameters of circles each having the same area as a projected area) of less than 30%. In JP-A-10-293372, a manufacture method is disclosed in which projected area diameters of tabular silver iodobromide grains are monodispersed through formation of silver halide nuclei with a high silver chloride content in a nucleation step. As described above, advance in technique for forming tabular silver iodobromide grains has made possible to obtain silver iodobromide emulsions having a narrow distribution of silver iodide contents between grains and silver iodobromide emulsions having a small variation coefficient of projected area diameters. However, to further enhance sensitivity, silver halide grains having a larger size and/or silver halide grains having a larger aspect ratio (projected area diameter/thickness) are desired. Particularly, as emulsions for blue-sensitive layers, silver halide tabular grain emulsions are desired which have a high silver iodide content, a large size and/or a large aspect ratio, a small distribution of silver iodide contents and a small distribution of projected area diameters.
A principal object of the present invention is to provide a silver halide photographic emulsion containing silver halide grains excellent in photographic properties, particularly, sensitivity/granularity, sharpness, gradation and the like, the emulsion being an emulsion of tabular silver halide grains having a high silver iodide content, a large size and/or aspect ratio, a small distribution in silver iodide content and a small distribution in projected area diameter; the emulsion is henceforth also called an xe2x80x9cemulsion of the present invention.xe2x80x9d
The task of the present invention has successfully been attained by the following approaches:
(1) A silver halide emulsion containing a dispersion medium and silver halide grains, wherein the silver halide grains have a variation coefficient of projected area diameters of 30% or less and 50% or more of the total projected area of the silver halide grains is occupied by silver halide grains satisfying the following requirements (a), (b), (c) and (d):
(a) a hexagonal tabular silver halide grain having a smooth (111) face as a principal plane;
(b) the silver iodide content is 7 mol % or more;
(c) the projected area diameter is 3 xcexcm or more; and
(d) the aspect ratio is 8 or more.
(2) The silver halide emulsion according to item (1) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (e) below as well as requirements of from (a) to (d):
(e) the ratios of the areas of (100) faces relative to the average area of the side surface calculated from the average projected area and the average thickness of all the grains are 50% or more.
(3) The silver halide emulsion according to item (1) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (f) below as well as requirements of from (a) to (d):
(f) the equivalent-sphere diameter is 1.2 xcexcm or more.
(4) The silver halide emulsion according to item (2) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (f) below as well as requirements of from (a) to (e):
(f) the equivalent-sphere diameter is 1.2 xcexcm or more.
(5) The silver halide emulsion according to item (1) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (g) below as well as requirements of from (a) to (d):
(g) the grains have at least ten dislocation lines per grain.
(6) The silver halide emulsion according to item (2) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (g) below as well as requirements of from (a) to (e):
(g) the grains have at least ten dislocation lines per grain.
(7) The silver halide emulsion according to item (3) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (g) below as well as requirements of from (a) to (d) and (f):
(g) the grains have at least ten dislocation lines per grain.
(8) The silver halide emulsion according to item (4) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (g) below as well as requirements of from (a) to (f):
(g) the grains have at least ten dislocation lines per grain.
(9) The silver halide emulsion according to item (1) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (d):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(10) The silver halide emulsion according to item (2) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (e):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(11) The silver halide emulsion according to item (3) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (d) and (f):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(12) The silver halide emulsion according to item (4) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (f):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(13) The silver halide emulsion according to item (5) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (d) and (g):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(14) The silver halide emulsion according to item (6) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (e) and (g):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(15) The silver halide emulsion according to item (7) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (d), (f) and (g):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(16) The silver halide emulsion according to item (8) above, wherein the silver halide grains occupying 50% or more of the total projected area satisfy requirement (h) below as well as requirements of from (a) to (g):
(h) the grains have, in their vertex portions and/or peripheral portions and/or principal plane portions, at least one epitaxial junction per grain.
(17) The silver halide emulsion according to any one of items (1) to (16) above, wherein, during its production, the growth of the grains corresponding to at least 50% of the whole silver amount is carried out by adding, at the same time as the addition of an aqueous silver salt solution and an aqueous halide salt solution, silver iodide fine grains and/or silver iodobromide fine grains formed outside a vessel in which the growth is being conducted to the vessel.
(18) The silver halide emulsion according to item (17) above, wherein the silver iodide fine grains and/or the silver iodobromide fine grains are added while being prepared continuously to a reaction vessel in which the growth of the grain is carried out.
(19) A silver halide photographic lightsensitive material comprising at least one silver halide emulsion layer on a support, wherein at least one of the emulsion layers contains the silver halide emulsion according to any of items (1) to (18) above.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.